In vehicles, evaporative fuel which leaks into the air from a fuel tank, a carburetor float chamber, etc., is described as one of causes of air pollution because of the large content of hydrocarbons (HC). The evaporative fuel also contributes to fuel loss. In view of the above, various techniques are known as a prevention thereagainst, and there is available an evaporative fuel controller representative of one such technique. In this controller, evaporated fuel from the fuel tank is absorbed by a canister which contains an absorbent such as activated carbon. When an engine is run, the absorbed fuel is released (purged) from the canister so as to be supplied to the engine.
One example of the above-described evaporative fuel discharge-preventing device for an engine is disclosed by published Japanese Patent Application Laid-Out No. 5-332205. According to the evaporative fuel-treating device taught in the aforesaid publication, a plurality of purge control valves are arranged in a side-by-side array in a purge passage which interconnects a canister and an air intake passage of an internal combustion engine on a downstream side of a throttle valve. While effecting control of a purge amount, the plurality of purge control valves causes evaporated fuel stored in a canister to be purged into the air intake passage in order to treat the fuel therein. A first valve control means performs duty control such as to open and close at least one of the purge control valves within a fixed duty cycle. A second valve control means provides control such as to open and close the other purge control valves on a duty cyclic basis. This construction holds or controls pulsation, and prevents vapor from flowing into a particular cylinder which would otherwise disturb the air-fuel ratio.
Another example is disclosed by published Japanese Utility Model Application Laid-Out No. 2-144657. According to a casing device for an engine taught in the above publication, the engine has a cam pulley connected to a forward end of a cam shaft so as to transmit a revolving force from a crankshaft via a belt which is trained around the cam pulley. A belt cover for covering the cam pulley and the belt is mounted on a front wall of a cylinder head of the engine. A transversely extending-through-gap is formed between the preceding front wall and a back wall of the belt cover. The gap has piping provided therethrough for distributing the fuel and the like.
In conventional evaporative fuel discharge-preventing devices for engines, the evaporative fuel generated in the fuel tank is temporarily absorbed by the canister; the absorbed, evaporative fuel is liberated (purged) from the canister during engine operation or vehicle traveling. The evaporative fuel is thereby supplied to the engine, together with fresh ambient air. At this time, negative pressure in an air intake pipe draws the evaporative fuel and outside air, i.e., ambient air.
However, an increase in size of the canister increases the amount of the evaporated fuel which is supplied to the engine.
As a result, the increased amount of the evaporated fuel to be supplied to the engine involves a disturbance of engine air-fuel ratio control. This causes an inconvenience, which is disadvantageous in view of practical use, in that engine rotational speed is unbalanced, with concomitant aggravation of drivability.
In order to obviate the above-mentioned inconveniences, the present invention provides an evaporative fuel discharge-preventing device for an engine having a canister provided midway along an air communication passage which intercommunicates the inside of a fuel tank and an air intake passage of an engine intake manifold, and a purge valve provided midway of the air communication passage between the canister and the intake manifold, in which the canister absorbingly retains evaporated fuel during stopping of the engine, the evaporated fuel being generated in the fuel tank, but releases the absorbingly retained fuel from the canister during operation of the engine by fresh air being introduced into the canister, whereby the evaporated fuel is supplied to the air intake passage, the improvement comprising a surge tank of a predetermined volumetric capacity being disposed midway of the air communication passage between the intake manifold and the purge valve, which tank is located at a position greater in height than the intake manifold.
Furthermore, the present invention provides an evaporative fuel discharge-preventing device, as aforesaid, wherein the surge tank has an outlet side pipe positioned at a lower portion thereof and an inlet side pipe located at a position above the outlet side pipe.
According to the present invention having the above structure, fluctuations in the amount of the evaporated fuel are made even by the surge tank which is placed midway along the air communication passage between the intake manifold and the purge valve. Consequently, a stabilized engine rotational speed is provided, which prevents degradation in drivability.
Furthermore, the surge tank has the outlet side pipe provided at a lower portion thereof and the inlet side pipe situated at a position above the outlet side pipe. Such a height position, at which the outlet and inlet side pipes are arranged, provides a smooth flow of coagulated evaporative fuel through the inside of the surge tank. This feature avoids storing the evaporated fuel in a state of liquid within the surge tank.